The degradation of building materials and structures such as historic buildings has currently presented a problem of great interest in order to preserve such buildings for posterity. Such degradation can be attributed to the presence of contaminants and chemical changes in the constituent building materials. In order to determine the nature and extent of the changes in building materials, maps reflecting the presence and distribution of contaminants and chemical changes can provide a very important tool in determining the methods of preservation and restoration which may become necessary as the structures continue to age.
While non-destructive testing techniques involving the use of neutron or gamma ray sources in conjunction with gamma ray detectors are generally known for detecting the characteristics and/or concentration of elements in an extended layer or medium, what is required is an improvement in such techniques for providing maps over an extended area of a relatively thick wall showing water concentrations as reflected by the presence of hydrogen and salt concentrations as reflected by the presence of chlorine. Following the mapping of the contaminant distribution, several different types of treatment can be utilized. For example, poultices can be applied to the surface of the building materials and the contaminants removed thereby. The effectiveness of the removal can be determined by repeating the mapping of the wall surface after treatment. Another method which can be employed is the diffusion of monomers into the materials, thus filling the regions where the destructive action of water and salt have changed the chemical composition and left voids. These voids can compromise the structural integrity of the structure. However, heat polymerization must, for example, be used to solidify the structure and an incomplete diffusion of the monomer into the building materials can present an additional problem. This additional problem relates to inadequate drainage. If the monomer is polymerized only on the surface portions of the wall, the water content of the walls could be trapped within the walls rather than being allowed to evaporate and/or drain. In any event, a non-destructive mapping technique is more highly desirable than making core drillings into the wall or other extended medium and the materials thereafter removed for chemical analysis in a laboratory. The coring techniques are thus destructive and samples only relatively small areas. While certain neutron albedo techniques have also been used to determine hydrogen content in materials, such methods are only sensitive to high concentrations of hydrogen and thus cannot be used over the range of concentration interest in building materials.